stop arm from walking

[archiver]

Posted by bill whitley at 2/11/2001 9:35 PM EST


Student on team #70, Auto City Bandits, from Powers Catholic High School and Kettering University.



Our current design allows our arm to walk at the shoulder joint. We are using both Fischer Price motors & gearboxes. Is there a way to keep the arm from backdriving the motors? I'm looking for something anywhere from a specific solution to general ways to keep arms from walking. All advice is appreciated.

Bill
Team #70
"Who says you need engineers when you have chiefdelphi.com?"

[archiver]

Posted by Jimmy Holmes at 2/11/2001 9:53 PM EST


Coach on team #27, Team RUSH, from Osmtech Academy and Textron.


In Reply to: stop arm from walking
Posted by bill whitley on 2/11/2001 9:35 PM EST:




"Who says you need engineers when you have chiefdelphi.com?"

Bill,
There are many ways to do this, but two come to mind. You could try putting the brake on the speed controller(im not the biggest fan of that one) or you could attach a cable to the arm and run it over a pulley at the pivot point arm then attach it to surgical tubing and a fixed point. You can then adjust the tubing to the point that the arm doesnt fall. The cable will travel along the pulley as the arm moves.
Just a thought...gl, Jimmy/T#27

[archiver]

Posted by Joe Johnson at 2/11/2001 9:58 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: stop arm from walking
Posted by Jimmy Holmes on 2/11/2001 9:53 PM EST:



Counter balance is a very important way to keep your
arm from falling.

Another way is to use a feedback loop. Put a
potentiometer tells your RC what position the arm is
in, then have the PBASIC code hold the arm in a
stationary position. There are limits to what you can
do with this but it can definitely make your robot
behave better.

Joe J.

[archiver]

Posted by Matt Berube at 2/12/2001 9:43 AM EST


Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.


In Reply to: counter balance and feedback
Posted by Joe Johnson on 2/11/2001 9:58 PM EST:



Using a pot and having your controller hold the arm in a position works great.

The thing you have to remember tho is that the power will be off at the end of the match. If you can get your arm to stay put with no power that might be an advantage.

I am a big fan of the gas struts in the small parts book. (page 226)

Matt B.
T49
"The Plastic Fantastic :=p)

[archiver]

Posted by Ed Sparks at 2/13/2001 6:18 PM EST


Engineer on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.


In Reply to: Re: counter balance and feedback
Posted by Matt Berube on 2/12/2001 9:43 AM EST:



I'm with Matt on this one. Gas shocks (you can add 'em, delete 'em, series 'em, parallel 'em until balanced) along with a closed loop control.

[archiver]

Posted by Al Skierkiewicz at 2/13/2001 2:12 PM EST


Engineer on team #111, Wildstang, from Wheeling High & Rolling Meadows High and Motorola.


In Reply to: stop arm from walking
Posted by bill whitley on 2/11/2001 9:35 PM EST:



Bill,
We have occassionally added a locking mechanism to hold a robot part in place. A servo that slips in a locking pin or a clutch assembly are things that jump to mind. Some of the motors (window motors for instance) hold position when off fairly well.
Al

[archiver]

Posted by Bob Drexel at 2/14/2001 8:29 PM EST


Engineer on team #358, Titans, from Hauppauge and Festo Corp..


In Reply to: stop arm from walking
Posted by bill whitley on 2/11/2001 9:35 PM EST:



I have been thinking about a solution to this also. We won't need to use it due to redesigns with our arm drive but I think a good solution is to make a centrifugal brake. If the motor shaft is extended long enough, a pair of arms with weights connected to the shaft can be used to compress a spring. So, when the motor is not running the spring can press on a friction material holding the motor shaft. When the motor starts to run the mass of the weights swing out due to centrifugal force compressing the spring.

You’ll have to work out the forces needed, but I think this basic idea has merit.